Short Circuit Problem

H

hsn6827

Member
Hello everybody,

I have a problem with my Teensy 4.1 board. Today, while i was trying some codes with RC servos, one analog signal wire was touched to servo's GND or +12V mistakenly and caused short circuit. Now, my teensy board does not run. When I energized it via USB, marked component with red rectangle below is becoming hot. What is this component? Any idea? Is it possible to repair it ?
 

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That part is the voltage regulator. It gets burning hot when another part of the board is shorted (from 3.3V to GND), because the rest of the board is trying to consume nearly limitless current and the regulator tries to work as hard as it can to supply that current.

I'm afraid the news is only bad.

Sometimes a 3.3V-GND short on the board is recoverable when the problem is stray metal, like excess solder. But when the 3.3V-GND short is inside a chip, repair isn't feasible. If you have a voltmeter, you could try measuring the DC voltage from 3.3V to GND. If you see a low number but not close to zero, like 0.5 to 0.9 volts, that's a pretty sure sign the short on your board is a semiconductor short. Metal shorts read zero or only a few millivolts.

Sadly, we've seen this many times with 12 volt projects. Accidentally touching 12 volts to pretty much anywhere, even for only the slightest moment, completely destroys the main processor. It's a sad moment to lose hardware, but at least you can avoid wasting a lot of time on attempting repair and just replace the entire board.
 
PaulStoffregen said:
That part is the voltage regulator. It gets burning hot when another part of the board is shorted (from 3.3V to GND), because the rest of the board is trying to consume nearly limitless current and the regulator tries to work as hard as it can to supply that current.

I'm afraid the news is only bad.

Sometimes a 3.3V-GND short on the board is recoverable when the problem is stray metal, like excess solder. But when the 3.3V-GND short is inside a chip, repair isn't feasible. If you have a voltmeter, you could try measuring the DC voltage from 3.3V to GND. If you see a low number but not close to zero, like 0.5 to 0.9 volts, that's a pretty sure sign the short on your board is a semiconductor short. Metal shorts read zero or only a few millivolts.

Sadly, we've seen this many times with 12 volt projects. Accidentally touching 12 volts to pretty much anywhere, even for only the slightest moment, completely destroys the main processor. It's a sad moment to lose hardware, but at least you can avoid wasting a lot of time on attempting repair and just replace the entire board.
Click to expand...
Thank you very much Paul. When I measure the 3V-GND pins DC voltage, I saw that 0.08 V. It is almostly closer to 0 VDC. So do you have any comment about it?
 
That is pretty close to zero. If you didn't know what went wrong, and especially if the problem had appeared right after soldering pins or doing some other mechanical work where stray metal may have been placed on the circuit board, I would have normally have suggested looking for a metal short.

But you do know what happened. Accidentally touching 12 volts isn't going to make metal magically appear. But it definitely will burn the inside of the main processor. We know this with good certainty because it's happened many times with people building 12 volt projects. The result is always the same, the U1 chip destroyed.

I know it's bad news, but hopefully not as painful as wasting a lot more time trying fix something that has virtually no hope of repair. It's time to just replace the damaged hardware.

Probably not very comforting, but plenty of other folks working with 12V have had similar mishaps. I've even done a couple times. Usually after something like this happens it's a good idea to think about connectors or cable (zip) ties or other ways to keep higher voltage wires secured while working on the hardware. Just 1 brief errant moment is all it takes to completely destroy the main chip.
 
Tips for a bulletproof setup:
  1. Use a poly fuse at least for low current applications, or a miniature circuit breaker for more demanding amps.
  2. When dealing with higher voltages than the MCU, the safest thing to do is use optical isolation. Both digital and analog options exist, at all sorts of speeds.
  3. Use a crowbar circuit to immediately cut off the voltage if it goes too high. This is what I have been doing on my projects/products that deal with different voltages. it's very simple to construct. It works by shorting supply to ground, and that's where the fuse/breaker comes into play.
  4. Use a diode to prevent the usual stupid mistake that I make, to prevent hooking up power backwards. I usually set it up so it will trip the fuse like the crowbar does, or at the input if there's a regulator following the input.
 
PaulStoffregen said:
That is pretty close to zero. If you didn't know what went wrong, and especially if the problem had appeared right after soldering pins or doing some other mechanical work where stray metal may have been placed on the circuit board, I would have normally have suggested looking for a metal short.

But you do know what happened. Accidentally touching 12 volts isn't going to make metal magically appear. But it definitely will burn the inside of the main processor. We know this with good certainty because it's happened many times with people building 12 volt projects. The result is always the same, the U1 chip destroyed.

I know it's bad news, but hopefully not as painful as wasting a lot more time trying fix something that has virtually no hope of repair. It's time to just replace the damaged hardware.

Probably not very comforting, but plenty of other folks working with 12V have had similar mishaps. I've even done a couple times. Usually after something like this happens it's a good idea to think about connectors or cable (zip) ties or other ways to keep higher voltage wires secured while working on the hardware. Just 1 brief errant moment is all it takes to completely destroy the main chip.
Click to expand...
Thank you for your suggestion and advice. As you mentioned or estimated in your post, yes I didn't use connector to connect my servos to power supply. It was possible risk for short circuit. Thus it happened. Ok. No need to spend time for recover. It is better to new one even it is expensive :(
 
xxxajk said:
Tips for a bulletproof setup:
  1. Use a poly fuse at least for low current applications, or a miniature circuit breaker for more demanding amps.
  2. When dealing with higher voltages than the MCU, the safest thing to do is use optical isolation. Both digital and analog options exist, at all sorts of speeds.
  3. Use a crowbar circuit to immediately cut off the voltage if it goes too high. This is what I have been doing on my projects/products that deal with different voltages. it's very simple to construct. It works by shorting supply to ground, and that's where the fuse/breaker comes into play.
  4. Use a diode to prevent the usual stupid mistake that I make, to prevent hooking up power backwards. I usually set it up so it will trip the fuse like the crowbar does, or at the input if there's a regulator following the input.
Click to expand...
Thank you very much for your very beneficial advices @xxxajk . They are very important tips. I have added some of them like using diodes to prevent reverse polarity troubles. But I will add fuse and crowbar circuit to circuit to increase protection.
Additionally to this list, do not any wiring or hardware changing without cutting energy from the circuit. :)
 
hsn6827 said:
Thank you very much for your very beneficial advices @xxxajk . They are very important tips. I have added some of them like using diodes to prevent reverse polarity troubles. But I will add fuse and crowbar circuit to circuit to increase protection.
Additionally to this list, do not any wiring or hardware changing without cutting energy from the circuit. :)
Click to expand...
You are quite welcome. If you need a schematic for the crowbar circuit, let me know.
 
hsn6827 said:
Yes, if you have an example, could you share it with me please?
Click to expand...
Sure, here's one.
NOTES:
SCR trip voltage is 400mV, you may need to adjust R1 to a lower value to decrease sensitivity.

Code: 
volts    D1        R1    trips at
3.3v     1N5333     60K    3.49V
5.0v     1N5228     60K    6.09V
Screenshot_20250523_104817.png
 
xxxajk said:
Sure, here's one.
NOTES:
SCR trip voltage is 400mV, you may need to adjust R1 to a lower value to decrease sensitivity.

Code: 
volts    D1        R1    trips at
3.3v     1N5333     60K    3.49V
5.0v     1N5228     60K    6.09V
View attachment 37606
Click to expand...
Thank you very much @xxxajk . But if you have full circuit, could you share it please? I could not understand that how i can place this diagram to my circiut.
 
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